JPS60130495A - Conductive paste - Google Patents

Abstract

PURPOSE:To obtain a conductive paste having excellent printability, solderbility and conductivity by preparing the paste of a resin consisting essentially of a prepolymer having a limited number average mol.wt. and the copper powder composed of flake copper powder and composite copper-silver powder limited in grain size and mixing ratio as a conductive material. CONSTITUTION:A conductive paste consists essentially of a resin A consisting essentially of a prepolymer having >=10,000 number average mol.wt. and copper powder B consisting of flake copper powder and composite copper-silver powder having <=10mum grain size and contains 75-90wt% the copper powder by the weight of the main components A+B. A phenoxy resin, polybutadiene resin, P- biphenyl resin, etc. are used as the resin A. An amino resin etherified by lower alcohol may be used in said resin by mixing said resin therewith or bringing said resin into reaction therewith. The resin A and the copper powder B are kneaded with a solvent, by which the conductive paste is prepd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a conductive paste having excellent printability, good solder adhesion, and excellent conductivity.

[Technical background of the invention and its problems] Conductive paste is a paste made by mixing a specified curable resin prepolymer with a conductive substance such as copper powder. When printed and cured, the cured surface has excellent conductivity and can be melted and coated with solder. For this type of conductive paste, curable resin prepolymers such as phenol resins, melamine resins, xylene resins, and epoxy resins having a number average molecular weight of about 100 to 2,000 are currently used to mix metal powder. Such conductive pastes are used for electrodes of electronic parts, printed circuits for conductor parts, and the like.

However, in recent years, electronic parts have become lighter, thinner, shorter, smaller, higher performance, and more dense, and there are demands for various improvements in conductive pastes. In other words, it has good printability, excellent solder adhesion,
In addition, a material with favorable conductivity is required. In reality, such conductive paste is not readily available.

[Object of the Invention] The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a conductive paste having excellent printability, solder adhesion, and good conductivity.

[Summary of the Invention] In the present invention, as a result of intensive research to achieve the above-mentioned object, it was discovered that the conductive paste described in (2) below can achieve the object. That is, the present invention comprises a resin (A) mainly consisting of a prepolymer with a number average molecular weight of io, ooo or more, a flaky copper powder (a) with a particle size of 10 μm or less as a conductive substance, and a copper/silver composite. A conductive paste containing a copper powder (B) consisting of a powder (B) as a main component, and containing the copper powder in an amount of 75 to 90% by weight based on the main component [(A)+(B)]. It is.

Examples of the resin (A) mainly composed of a prepolymer having a number average molecular weight of 10,000 or more used in the present invention include phenoxy resin, polybutadiene resin, p-vinylphenol resin, epoxy-modified acrylic resin, and 1,2-polybutadiene resin. etc., and these can be used alone or in combination of two or more.

This resin may be used by mixing or reacting with an amine resin etherified with a lower alcohol such as methanol, ethanol, butanol.

The reason why the resin has a number average molecular weight of io, ooo or more is 1.
This is because if it is less than 0.000, high-density packing of the copper powder becomes impossible, and the paste does not form, making it unsuitable for screen printing and the like.

As the copper powder (B) used in the present invention, flaky copper powder (a) and copper/silver composite powder (b) are used. All of these powders preferably have an average particle size of 10 μm or less. If it exceeds 10 μm, it is not preferable because high-density filling becomes impossible, the paste does not form, and printability deteriorates. The flaky copper powder (a) is not particularly limited as long as it has an average particle size of 10 μm or less, and any commercially available powder can be used. In addition, the copper/silver-based composite powder (b) in the present invention refers to the surface of copper powder, such as one in which 0.3 to 20% by weight of metallic silver is precipitated on the surface of copper powder using a silver complex salt solution. coated with silver. If the precipitated proportion of metallic silver is less than 0.3% by weight, it has no effect on conductivity, and if it exceeds 20% by weight, not only will the cost increase, but the conductivity will not be higher than that, which is undesirable. Therefore, it is limited to the above range. The mixing ratio of the flaky copper powder (a) and the copper/silver composite powder (b) is preferably 10/90 to 90/10 in ut ratio.

If the weight of the flaky copper powder is less than 10, it will not form a good paste, and if it exceeds 90, the conductivity will be poor, which is not preferable.

The conductive paste of the present invention has resin (A>) and copper powder 5-(B) as its main components, and the blending ratio of the copper powder must be 75 to 90% by weight based on the main components.

If the copper powder content is less than 75% by weight, solder adhesion will be poor, and if it exceeds 90% by weight, the adhesion will be poor and the coating film will be brittle, which is not preferable. Therefore, it is limited to the above range.

A conductive paste is prepared by adding a small amount of a solvent such as butyl carpitol acetate to the main component thus obtained and kneading it using a triple roll or the like.

The object to which the conductive paste of the present invention is applied is resin,
Any insulating base material, metal plate, etc. may be used, and roll coater,
Apply by screen printing, etc.

This curing is 80 to 25% when the resin content is thermosetting resin.
This is done by heating to 0°C. When the resin is composed of an amino resin, a polybutadiene resin, a p-vinylphenol resin, a polyester resin, or the like, heating causes a condensation reaction between the amine resin and the hydroxyl groups of the resin prepolymer to form a three-dimensional network structure.

In this process, the copper powders come into contact with each other and are connected, resulting in conductivity. Solder can be roughly melted on the hardened surface of this coating. The hardened surface has good solder wettability, so it has excellent solder adhesion.

The reason for this is not clear, but it is thought that the interaction between the amine resin as a crosslinking agent and the solder surpasses the solder repellency. Therefore, a good conductive surface can be obtained, and it can be used, for example, as a printed circuit in which various mounted products are combined. To melt and coat the cured surface of the conductive paste of the present invention with solder, it may be brought into contact with a molten solder bath, or the solder or solder cream may be heated and melted on the cured surface.

"Examples of the Invention" The present invention will be specifically explained with reference to Examples. Hereinafter referred to as "Part"
means "parts by weight", and the present invention is not limited to this example.

Example 1 30 parts of flaky electrolytic copper powder with an average particle size of 10 μm and 0
．． 45 parts of 5% silver-plated copper powder and a number average molecular weight of 14
000 phenoxy resin, 1 part of methyl etherified melamine resin, and 15 parts of butylcarpitol acetate as a solvent were thoroughly kneaded using a ceramic Mikino mold to obtain a conductive paste (A).

Example 2 Number average molecule instead of phenoxy resin in Example 1! 20
Conductive paste 1 (B) was obtained in exactly the same manner as in Example 1 except that 000 isophthalic acid polyester resin was used.

Comparative Example 1 30 parts of flaky electrolytic copper powder with an average particle size of 10 μm and 0
．． 45 parts of 5% silver-plated copper powder and a number average molecular weight of 38
0.00 epoxy resin and 0.00 parts of imidazole crosslinking agent.
5 parts and a small amount of butylcarpitol acetate as a solvent are thoroughly kneaded with three rolls to make a conductive paste (C)
I got it.

Comparative Example 2 A conductive paste (D) was obtained in the same manner as in Example 2, except that 80 parts of flaky electrolytic copper powder having an average particle size of 10 μm was used as the copper powder.

Using the conductive pastes obtained in Examples and Comparative Examples, an epoxy laminate (MEL-4 manufactured by Toshiba Chemical Corporation) was printed using a screen printing machine with a 180 mesh screen.
(trade name) on which a pattern with a width of 1 + nn + total length of 20 cm was printed. Next, heat cure at 180℃ for 1 hour to a thickness of 20℃.
A hardened paste surface of μm was obtained.

After applying solder flux to this cured surface, solder of 63% tin containing 0.5% copper was melted and adhered at 240° C., and the state of the paste, printability, solder adhesion, and conductivity were tested. The results are shown in Table 1.

[Effects of the Invention] The conductive paste of the present invention has good printability, good soldering adhesion, and paste condition, and has excellent conductivity, and is suitable for printed circuits and the like.

Patent applicant: Toshiba Chemical Corporation 10-

Claims (1)

[Claims] 1. A resin (A) mainly consisting of a prepolymer with a number average molecular weight of 10,000 or more, and a conductive substance with a particle size of 10,000 or more.
The main component is a copper powder (B) consisting of a flaky copper powder (a) of μm or less and a copper/silver composite powder (b), and the copper powder is the main component [(A) + (B)] 75 against
A conductive paste characterized by containing ~90% by weight. 2. The conductive paste according to claim 1, wherein the resin (A) comprises a prepolymer having a crosslinkable hydroxyl group and an amine resin etherified with a lower alcohol. 3 The mixing ratio [(a)/(b)] of the flaky copper powder (a) and the copper/silver composite powder (b) of the copper powder (B) is 10
The conductive paste according to claim 1 or 2, wherein the conductive paste has a weight ratio of /90 to 90/10 (weight ratio). 4. Claims 1 to 4, characterized in that the copper/silver-based composite powder (b) is obtained by substituting 0.3 to 20% by weight of metallic silver on the surface of copper powder using a silver complex salt solution. The conductive paste according to any one of Item 3.